<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>引入外部js</title>
    <!--引入外部的js文件-->
    <script type="text/javascript" src="test.js"></script>
</head>
<body>
<input type="button" value="点击" id="btn" >
</body>
</html>